Processes have been developed for the partial combustion of various liquid and gaseous hydrocarbons, e.g., methane, residual oil, etc., with an oxygen-containing gas to produce synthesis gas, i.e., a gas containing primarily hydrogen and carbon monoxide. The product synthesis gas contains significant amounts of free carbon in the form of soot, particularly when heavy hydrocarbons are employed as feedstock. Various processes have been developed for the separation and recovery of this soot. One method involves scrubbing the product gas with water to produce a water-soot slurry. The slurry is then treated with a light hydrocarbon oil, e.g., naphtha, to produce a phase separation, i.e., water and naphtha-soot phases. The naphtha-soot phase is then treated to separate and recover the naphtha and soot. Descriptions of such processes can be found in U.S. Pat. Nos. 2,992,906; 3,473,903; 3,694,355 and 3,917,569.
In a naphtha recovery process used in the art the naphtha-soot slurry is mixed with a heavy liquid hydrocarbon, e.g., residual oil, heated, then distilled, e.g., by steam stripping, and condensed to recover the naphtha. The bottoms, a residual oil-soot slurry can then be recycled as the raw material for the partial oxidation process. Further details on this naphtha recovery process can be found in U.S. Pat. No. 3,473,903.
When the art process is used with heavy hydrocarbon liquids such as residual oil, several problems occur. The energy requirements of the process are high because the residual oil must be heated above the normal boiling temperature of the naphtha to reduce the naphtha content of the stripper bottoms. Furthermore, most of the superheat present in the naphtha vapors is not utilized; and this results in a loss of useable energy. Finally, entrained residual oil may cause fouling of conventional heat exchanger surfaces in the system.